As an optical device of this type, there is known an optical device in which two capillary tube/lens assemblies each having a capillary tube, to which an end portion of an optical fiber is fixed, and a lens, which are fixed to a common sleeve by an adhesive or the like, are provided and fixed to an inside of an accommodation member (cylindrical member or cabinet) so that the lenses are opposed to each other through an intermediation of an optical functional component (such as optical filter or optical isolator core) (for example, the following Patent Literatures 1 to 4). The lens has functions of collimating light output from the optical fiber into parallel and of collecting the parallel light to allow the collected light to input into the optical fiber. As the lens, for example, there may be used: a cylindrical lens of a refractive index profile type (so-called GRIN lens: one end is a vertical surface perpendicular to an optical axis, and the another end is an inclined surface in many cases); a cylindrical lens having a uniform refractive index, in which two partial spherical lens surfaces having the same center curvature are provided on both ends (so-called drum lens); a cylindrical lens having the uniform refractive index, in which the partial spherical lens surface is provided on one end (so-called C lens: another end is inclined surface in many cases); and an aspherical lens.
Further, in Patent Literature 5 described below, in order to enable optical axis adjustment between an optical fiber and a lens, a capillary tube assembly in which a capillary tube (ferrule) to which an end portion of the optical fiber is fixed is embedded in a recessed portion of a sleeve and a lens assembly in which a lens fixed to an inside of a cylindrical bush are produced, relative positions of the capillary tube assembly and the lens assembly are adjusted, to thereby perform optical axis adjustment between the optical fiber and the lens, and then an end surface of the sleeve and an end surface of the cylindrical bush are fixed to each other. A leading end surface of the optical fiber and an end surface of the capillary tube retaining the optical fiber is polished to form a spherical shape and the capillary tube is pressed by the sleeve, thereby allowing the leading end surface of the optical fiber to be brought into physical contact (PC contact) with an incident/emission surface of the lens. As the lens, the GRIN lens is used. Besides, a filter serving as the optical functional component is fixed to a member (base member 7b) which is separate from the lens assembly to be interposed between lens assemblies which are opposed to each other.
Further, in the following Patent Literature 6, various optical components such as a band pass filter and the optical isolator are each fixed to a separate cylindrical sleeve having an outer diameter corresponding thereto, to thereby produce a plurality of elements. Using a marker for position alignment formed on the cylindrical sleeve of the respective elements, the respective elements are aligned in positions with each other to be laminated and fixed (cylindrical main body). Then, the capillary tube assembly (ferrule assembly) is subjected to optical axis adjustment in X, Y, Z-axis directions and is fixed to one end of the cylindrical main body thus produced. An element having a spherical lens is subjected to the optical axis adjustment in the X, Y, Z-axis directions and is fixed to the another end of the cylindrical main body, and further an element having a capillary tube assembly (ferrule assembly) is subjected to the optical axis adjustment in the X, Y, Z-axis directions to be fixed. Further, there is disclosed as the above-mentioned element an element in which an aspherical lens press-fitted and fixed into the lens holder and a band pass filter are fixed to the cylindrical sleeve (FIG. 2A).